1. Technical Field
The present invention relates generally to the field of integrated circuits, and, more specifically to an on-chip thermal sensing circuit for measuring the temperature of integrated circuit chips and particularly microprocessor chips.
2. Description of Related Art
It is important to be able to monitor the temperature of an integrated circuit (IC), particularly those implemented using CMOS designs. At higher temperatures, the IC's characteristics change. Circuits get slower, and reliability decreases. Thus, it is important to monitor the temperature of integrated circuits, and in particular microprocessor chips.
It is known in the art for a microprocessor to attempt to manage its temperature by regulating the speed at which it processes. In order to manage its temperature, both external sensors and on-chip sensors have been used.
External sensors are those sensors that are not located on the integrated circuit itself. These sensors are not preferable, however, because they do not provide real-time results and are unable to measure the circuit temperature at the location on the chip of the highest power dissipating circuits.
There have been a number of prior art proposals for on-chip temperature sensing. These proposals include the use of a pair of on-chip thermally response diodes coupled to an off-chip current source. The diode pair generates a differential voltage output that is proportional to temperature. This technique for sensing on-chip temperatures requires numerous connections between the chip and external circuitry for each temperature sensing circuit. Each connection to the chip increases the cost of the product. Small, self contained on-chip temperature sensors have a much lower cost than sensors requiring connections to circuitry external to the chip.
Another prior art design utilizes an on-chip thermal sensor as part of a thermal assist unit. The thermal assist unit consists of three registers, a multiplexer, a latch, a decoder, an interrupt generator, and a thermal logic control block. The thermal sensor circuit utilizes the differential voltage change across two diodes biased at the same operating current, where one diode is larger than the other. For example, the voltage across the larger diode will decrease more quickly than the voltage across the smaller diode when the temperature increases.
It would be desirable to be able to measure localized heating of the chip. Therefore, a need exists for an on-chip thermal sensing circuit that may be replicated throughout the chip.